They should stay true to what Flash is as a character. IMO he's always been at his best when he was one of DC's more colorful characters, and they should stay true to that. My worst fear right now is that they will make a Flash movie but it will be so dark and gritty that you completely forget what a fun superhero The Flash can be. Given Geoff Johns' recent run on the comics I suppose I shouldn't be all that surprised if that's the direction they want to go in (especially since, like Johns, it sounds like they want to have Barry as the main character).
That's part of why I like Wally West. He really was basically the Peter Parker of the DC universe. He's funny, cool, a bit of a smartass, and has just as much drama to deal with when he's out of his costume as he does when he's wearing it. Right now it may be a bit of a longshot that we'll even get a Flash movie, let alone one with Wally since DC has kind of dropped him from "the cool club" lately, but hey, a guy's gotta hold out hope I suppose.
I think ideally, they should do a trilogy that starts with Barry, transitions from Barry to Wally, and then finishes with Wally. That way, everyone is happy. I don't want them to do a whole trilogy of Barry movies before they even consider doing Wally though, because then we probably won't see a movie with Wally as the Flash until 2020 at the earliest, if ever (since they could indefinitely stop making Flash movies after doing a trilogy, assuming they even make i that far). There's no guarantee that we'll even get a Flash film right now, let alone 4 of them, and that would be 3 movies of Barry I'd have to wait through before getting just one movie of Wally.
[blackout]Of course, if I were to advocate the most selfish route, I'd start with the movie that passes the torch from Barry to Wally, since I could live and die quite happily without ever seeing Barry get a "true" solo film, and on the chance that we only get one Flash movie I'd like to see some Wally action in there.[/blackout]